<!DOCTYPE html
    PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>鼠标移过，改变图片路径</title>
    <style>
        body,
        ul,
        li {
            margin: 0;
            padding: 0;
        }

        body {
            background: #000;
        }

        img {
            border: 0;
            border-radius: 3px;
        }

        ul {
            list-style-type: none;
        }

        #box {
            width: 212px;
            border: 5px solid #fff;
            overflow: hidden;
            zoom: 1;
            background: #fff;
            border-radius: 5px;
            margin: 10px auto;
            padding: 0 0 3px 3px;
        }

        #box li,
        #box li img {
            float: left;
            width: 50px;
            height: 50px;
        }

        #box li {
            margin: 3px 3px 0 0;
        }

        #box li.first {
            position: relative;
        }

        #box li.first,
        #box li.first img {
            width: 156px;
            height: 156px;
        }

        /* 用来加载图片，加载过程图片会有半透明效果 */
        /*    除了 position: absolute;和 position: fixed;会直接将元素从排版中拿走从而脱离文档流之外，设置float对象也会 “打乱这个排列”从而也被称为脱离文档流。*/
        #box li.first div {
            position: absolute;
            top: 0;
            left: 0;
            width: 156px;
            height: 156px;
            display: none;
            opacity: 0.5;
            filter: alpha(opacity=50);
            background: #fff url(img/loading.gif) 50% 50% no-repeat;
        }
    </style>
    <script type="text/javascript">
        window.onload = function () {
            let oImg = document.querySelectorAll('#box img')
            for (let i = 1; i < oImg.length; i++) {
                oImg[i].onmouseover = function () {
                    oImg[0].src = this.src.replace(/small/, 'big')
                }
            }
        };
    </script>
</head>

<body>
    <ul id="box">
        <li class="first">
            <img src="img/big_1.jpg">
        </li>
        <li><a href="javascript:;"><img src="img/small_1.jpg"></a></li>
        <li><a href="javascript:;"><img src="img/small_2.jpg"></a></li>
        <li><a href="javascript:;"><img src="img/small_3.jpg"></a></li>
        <li><a href="javascript:;"><img src="img/small_4.jpg"></a></li>
        <li><a href="javascript:;"><img src="img/small_5.jpg"></a></li>
        <li><a href="javascript:;"><img src="img/small_6.jpg"></a></li>
        <li><a href="javascript:;"><img src="img/small_7.jpg"></a></li>
        <li><a href="javascript:;"><img src="img/small_8.jpg"></a></li>
        <li><a href="javascript:;"><img src="img/small_9.jpg"></a></li>
        <li><a href="javascript:;"><img src="img/small_10.jpg"></a></li>
        <li><a href="javascript:;"><img src="img/small_11.jpg"></a></li>
    </ul>
</body>

</html>